<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <style>
        *{
            margin: 0px auto;
        }
        div{
            display:block;
            height: 60px;
            width: 300px;
            border: solid 1px #333;
        }
    </style>
</head>
<body>

测试
    <div>aaa</div>
 值
<h2>第二行</h2>
</body>
</html>